Combined magnetic transducer head and coupling transformer



Feb. 12, 1952 W|EGAND 2,585,065

COMBINED MAGNETIC TRANSDUCER HEAD AND COUPLING TRANSFORMER Filed Dec. 24, 194'? 2 SHEETS-SHEET 1 IIHMMMIMM Feb. 12, 1952 WEGAND 7 2,585,065

' COMBINED MAGNETIC TRANSDUCER HEAD AND COUPLING TRANSFORMER Filed Dec. 24, 1947 2 SHEETS-SHEET 2 fig. 6.

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Qy 7 I 2 Patented Feb. 12, 1952 COMBINED MAGNETIC TRANSDUCER HEAD AND COUPLING TRANSFORMER David E. Wiegand, Villa Park, Ill., assignor to Armour Research Foundation of Illinois Institute of Technology, Chicago, 111., a corporation of Illinois Application December 24, 1947, Serial No. 793,727

This invention relates to an electromagnetic transducer head, and more particularly, to what is generally known as a single-turn head with the turn going through the gap of the head.

Great improvements have been made in the magnetic recording field in recent years, and to some extent this has been brought about by the development of relatively high coercive force materials which could be formed into a wire or tape for use as a magnetic record member. It has been found that the maximum capabilities of high coercive force material can only be utilized when certain conditions are present. In the recording process, intense magnetic fields are required-and these intense fields are obtained by the present invention with a minimum amount of leakage flux which tends to demagnetize the high frequency. In other words, the effective scanning width of the recording gap is reduced, thus allowing the recording of higher frequencies.

A further feature of the present invention is the ability of heads designed in accordance with the teachings of the present invention to erase high coercive force material without overheating of the head structure. In general, intense magnetic fields in electromagnetic apparatus are obtained only by operating the electrical part of the apparatus at high current density. In the head structures of the present invention, the copper foil in the gap may be operated at extremely high current density because of its short length and because of rapid heat conduction to relatively heavy masses of copper to which the foil is attached at both ends. In this connection, the present invention is particularly advantageous in that the high current density is applied where it is needed the most, or, in other words, in the head gap close to the recording wire.

The head structures of the present invention are also particularly advantageous as play-back heads. In conventional play-back heads of the prior art, a compromise has been made in selecting the width of the head gap. As the width of the gap is decreased, the fineness of scanning is improved, but the leakage flux across the gap surfaces directly under the record member increases. Since this leakage flux does not thread the coil, a reduction in output voltage results. This effect is present for all frequencies. At high frequencies, there is an additional eifect in prior art head structures. When the head coil is loaded by a resistor, such as is commonly used in the input circuit of a play-back amplifier, or by the distributed capacitance of the coil itself in associated wiring, the resulting currents in the coil 7 6 Claims. (Cl. 17 9-1002) cause an increase in leakage flux. The effect is the same for a head without this additional leakage flux in series with an inductance. In the case of the resistance loading, the effect is a gradual falling ofi of the high frequencies. The efiect of the capacitance loading is to cause a resonant frequency beyond which the response of the head is extremely poor or nil. As a result of these series inductance effects, there is a limit to the number of turns that can be placed on a conventional pick-up head and, therefore, a limit on the voltage which can be supplied by thehead.

With a structure such as that of the present invention, part of the flux leaking across the gap and all of the flux leaking below the gap links the turn in the gap, and therefore, is just as eifective in producing voltage as the flux which follows the path of the core structure. The result is an increase in output voltage in medium and low frequencies, and also at high frequencies, since the effect of the apparent series inductance of the head'is greatly reduced. I

It is an object of the present invention to provide a novel electromagnetic transducer head which is efiicient in operation, and rugged and reliable in use. a

A further object of the present invention is to provide a novel electromagnetic transducer head which is particularly suited for use with relatively high coercive force materials, such, for example, as materials having a coercive force in excess of 300 oersteds.

A still further object of the present invention is to provide a novel single-turn electromagnetic transducer head.

Another and further object of the present invention is to provide a novel combination electromagnetic transducer head and transformer.

Still another and further object of the present invention is to provide a novel head which is suitable for use either as a recording head, a playback head or an erasehead.

The novel features which I believe to be characteristic of my invention are set forth with'particularity in the appended claims. My invention itself, however, both as to its organization, manner of construction, and method of operation, toe gether with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure l is a front elevation-a1 view of anelectromagnetic transducer headembodying the novel teachings and characteristics of the present invention;

ent embodiment of the present invention;

Figure 8 is a right end view of the embodiment of the invention shown in Figure 7 and Figure 9 is a top view of-the-electromagnetic transducer head shown in Figure '7.

Referring first to the formofc'the invention:

illustrated in Figures 1 to 6 of the drawings, the electromagnetic transducer head illustrated includes a head lamination H and a transformer core-l2; each made ofamagnetic-zmaterialihaving relatively high" permeability and-Irelatively low retentivity; The headrlamination .l I as: shown in Figure l :of the 'drawingsihas :an arcuate :top edge l3fwhich is slotted as at'.I4-'to receive a copperfoil-or: bar l5iwhichtextends;at right:angles to the plane 'ofi: the f ace.- of the core lamination i i Thetopredge-r I 3 :is. alsolugroovedas at I 6 to receive a'wirelor other threadalikezmagnetic record member. s(shown only in Figure fzl. The core i I; of course; acts as: a.-.ilowrmagnetic" reluctance path forztlie3magnetic field about'the current-carrying copperbarorfoillStand tends to concentrate the magnetic. field.- in'itheismail agap. l4-across which the' wire or: other: magnetic record iinember i l crosses,

The'transformer core. i 2 maybe of any suitable form; but preferablysis.a;laminated;sirnp1e rectangular shell type corghavinga-centerleg :8

upon: which two' pancak'encoils: l9 and 20 are mounted. Thesepancake-coils IB-and-Zil-lie on opposite sides of acopper-pla-te zl which in-the illustrated embodiment f vthe "present invention has the'shape as illustrated most clearly in Figures Sand 4 of thedrawings: This plate 2| has a central opening 22 which enablesrthe plate to straddle-the leg l8 of-the-transformer-core I2. The-plate 2lalso includestwo upstanding leg portions 23 and 24-whichstraddle the head lamination ll'asis clearly-shown in Figure l of the.

drawings.

The tops of the legs 23 and 24-are slotted as at 25: to -receive the copper-foil-or bar IS; the

bar I5 being secured. tothe legs 23 and 24by= solder or other suitable bonding and. electrically conductingmaterial. The' copper plate-2l thus,

in .conjunctionwith the copper fOilor'bar i5 acts as asingle-turn coilfor feeding energy to or-fromthe head, lamination H; Forexample, when theyelectromagnetic transducer-head is beingused to. make: a magnetic record: on the traveling record member: I'I, fluctuating electricenergy representing'thersignal -to be recorded is fed to'ithe pancakecoils |9-and these coils beingr the primary windings of the; coupling transformer which feeds energy to the head Fluctuating electric current 1 is lamination II. thus inducedi in the single-turn secondary formed by thencoppernplateil and-the copper bar IS. The. fluctuating electric current is of high current density, thus enabling good recording onhigh coercive force material used asthe record-member H.

The fluctuating electric current flowing through the bar l5 sets up a strong fluctuating magnetic field around the bar I5. This causes longitudinal magnetization of the travelin record member I! as it passes across the gap 14 in the head lamination II. On play-back, the reverse operation takes place. This same type of head may also be usedas an erase-head, and very satisfactory results are obtained in erasint high coercive force material.

In the form of the invention shown in Figures 7, 8 and'9 of the drawings, the head lamination and the transformer core are combined in a single structure 26 which is in the form of a single lamination having an arcuate top edge 21 grooved as at 28 to receive the traveling recordmember.

The single lamination 26 is a simple rectangular; core typecore piece and has the high impedancewinding 29 mounted on the lower part thereof? A U-shape strap 30 also extends through the rectangular opening 3| in the core 26- and straddlesthe-upper portion of-the-core 26. This U-shape copper strap -3!i"is slotted as at 32 to receive abar or copper foil 33which' extends through the slot 34 formed in the top edge 21 of the lamination 26. The-bar 33-is soldered or otherwise suitably electrically secured to the strap 30 as at 35. Thestrap 38." in conjunction with the bar- 33, thus forms a single-turn winding for the transformer which enables the use of high current density in the bar 33.

This second embodiment of the" present invention is not quite as effective from the stand-'- point of low leakage reactanceas'the firstform of the invention, since the single-turnis'not as closely linked to thehigh impedance coil, but it has the advantage that the parts of the copper strap 30 which lie parallel to the'side surfaces of the head lamination act as eddy currentshields and, therefore, serve to concentrate the flux in the record member;

While I have shown severalparticular embodiments of m invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made, and I, therefore, contemplate by the appended claims to cover'all such modifications as fall within the true spirit'and scope of my invention.

I claim as my-inventionz l. A' combined electromagnetic transducer head andtransformer'comprising a single core having anedgeth'ereof slotted-"to provide a pair of confronting poles over which a traveling magnetic record'member is arranged to pass, a

relatively 'high impedance winding on said core, and arelatively low impedance winding on said core, a portion of said'low impedance winding lying in said slot'and additional portions of said low impedance winding lying along either side of said' poles thereby providing eddy current shields which concentrate the flux in the record member.

2;: A combined electromagnetic transducer head and transformer comprising a single core having 'an'edge thereof slotted to provide a pair of-confrontingpoles over which a traveling magnetic rcord'member is arranged to pass, a relatively high impedance winding on said core, and

a single turn winding in the formof a'closed loop about said core, said single turn winding includ-' ing an elongated conductor lying in said slot and a C's-shape strap having the ends thereof secured to said conductor.

3. A combined electromagnetic" transducer head and transformer comprising a core of magnetic material having a central opening therein and having an edge thereof slotted to provide a pair of confronting poles over which a travelil'lg magnetic record member is arranged to pass, a relatively high impedance winding wound on said core at a point remote from said slot, a bar of conducting material seated in said slot and extending out of either side thereof, and a conducting strap extending through said opening in said core and up on both sides thereof in the region of said slot, said strap being electrically connected and secured to said bar.

l. A combined electromagnetic transducer head and transformer comprising a core of magnetic material having a central openin therein and having an edge thereof slotted to provide a pair of confronting poles over which a traveling magnetic record member is arranged to pass, a relatively high impedance winding wound on said core at a point remote from said slot, a bar of conducting material seated in said slot and extending out of either side thereof, and a conducting strap extending through said opening in said core and up on both sides thereof in the region of said slot, said strap being electrically connected and secured to said bar, said strap being substantially as wide as the width of said opening in said core.

5. A combined electromagnetic transducer head and transformer comprising a core of magnetic material having a central opening therein and having an edge thereof slotted to provide a pair of confronting poles over which a traveling magnetic record member is arranged to pass, a relatively high impedance winding wound on said core at a point remote from said slot, a bar of conducting material seated in said slot and extending out of either side thereof, and a conducting strap extending through said opening in said core and up on both sides thereof in the region of said slot, said strap being electric-ally connected and secured to said bar, the ends of said strap extending beyond the edge over which the travelling record member passes.

6. A combined electromagnetic transducer head and transformer comprisin a single core having a transformer core portion and a transducer head core portion, said transducer head portion including a pair of spaced poles with a non-magnetic gap therebetween, means establishing a magnetic path between said core portions, a relatively high impedance winding on said transformer core portion, a metal bar extending within said gap, and means including a single turn, electrically conductive member about said transformer core portion secured to said bar and magnetically coupled to said high impedance winding, said last named means providing a low impedance path for concentrating the magnetic field in the vicinity of said gap.

DAVID E. WIE'GAND.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,418,542 Camras Apr. 8, 1947 2,456,767 Camras Dec. 21, 1948 2,539,400 Camras Jan. 30, 1951 FOREIGN PATENTS Number Country Date 612,450 Germany Apr. 25, 1935 622,623 Germany Dec. 2, 1935 693,664 Germany July 16, 1940 880,550 France Mar. 29, 1943 

